The present invention relates to halogenated 4-aminophenols and to halogenated 4-(phenyldiazenyl)phenols, to a process for their preparation and to the use of the halogenated 4-hydroxyphenols for preparing active ingredients, especially in pharmaceuticals and agrochemicals.
Halogenated phenols, especially fluorinated phenols, are valuable starting materials for the preparation of active ingredients inpharmaceuticals and agrochemicals, since the fluorine substituents increase the lipophilicity and therefore the membrane permeability of the entire active ingredient molecule. For example, fluorinated 4-hydroxyanilines are particularly suitable as starting materials for preparing active ingredients which are used for treating chronic bronchitis (see also WO 03/08413 and PCT/03/02154).
The preparation, for example, of 2,5-difluoro-4-hydroxyaniline is typically effected by nitrating 2,5-difluorophenol and subsequently reducing (see JP-A 63 310850).
A disadvantage of this synthetic route is that the nitration reaction does not proceed selectively and the 4-nitrophenol desired as an intermediate is obtainable only in poor yields.
There is therefore a need to provide a process which enables the preparation of halogenated 4-aminophenols in good yields and in a simple manner.